The present invention relates to a motor capable of changing characteristics thereof, and particularly to a technique effectively applicable to a brushless motor.
Conventionally, in order to make current and/or commutation flow to an armature coil in a non-contact state by using semiconductor devices, a brushless motor is constructed such that an armature is used as a stator and a field magneton is used as a rotor. A magnet or electromagnet has been used as the field magneton. However, the field magnet on using a magnet has been mainly used because there is a need of making current and/or commutation flow in a non-contact state.
FIG. 9 is a view to explain a configuration of the above conventional brushless motor. An apparatus shown in FIG. 9 is a so-called outer-rotor type brushless motor. The brushless motor includes a stator 102 fixed to an end bracket 101, and a rotor 104 which is rotatably arranged over an outer periphery of a stator core 103 of the stator 102. The rotor 104 includes a bottomed cylindrical yoke 106 fixed to a rotor shaft 105, and magnets 107 arranged on an inner periphery of the yoke 106. These magnets 107 face the outer periphery of the stator core 103 via a predetermined air gap.
Further, the rotor 104 is provided with a sensor rotor unit 108 for detecting rotational positions thereof. In general, the sensor rotor unit 108 is constituted such that a ring magnet 110 is fixed to a sensor rotor 109 formed of non-magnetic materials (substances) such as aluminum, synthetic resin or the like. Contrary to this, a sensor unit 111 using Hall element or the like is provided at a position facing the ring magnet 110 in a side of the end bracket 101. In this case, the ring magnet 110 is magnetized up to the same number of (magnetic) poles as the magnets 107 of the rotor 104. Therefore, pole change in the ring magnet 110 is detected by the sensor unit 111, and thereby it is possible to know rotational positions of the rotor 104 rotating in a manner synchronous therewith.
On the other hand, a three-phase Y-connection motor winding (armature coil) 112 is wound around the stator core 103. Currents flow in each phase of the motor winding 112 in accordance with signals transmitted from the sensor unit 111 such that a rotating magnetic field is successively created from a driver circuit (not shown). By doing so, the rotor 104 is rotated over the periphery of the stator 102, and thereby the rotor shaft 105 is operated by rotation.
In this case, when a magnet is used as a magnetic field means, an effective magnetic flux is fixed in a magnetic circuit under the motor design. For this reason, motor characteristics are also specified at one kind in specifications of one winding in the case where a voltage is constant. FIG. 10 is a diagram showing characteristics of conventional brushless motor, and shows one example of characteristics of the case where a power-supply (source) voltage is 12V.
In FIG. 10, T means a motor torque, and N means the number of motor revolutions. As shown in FIG. 10, in the conventional brushless motor, if a voltage is kept constant, the torque and the number of revolution are uniquely determined. Thus, in the case of manufacturing appliances using the brushless motor, an operating point based on the above characteristics is determined.
In the case where the motor is used in a constant load state, there arises no problem even if the motor characteristics are fixed. However, in the case where the motor is effectively used under such a utilizing condition that the load state changes, there arise some disadvantage cases if the motor characteristics have been fixed.
For example, in a motor used for a small size electric vehicle, if it is assumed that the electric vehicle has no transmission for simplification, a xe2x80x9clow-rotation and high-torquexe2x80x9d type is desired as a motor characteristic at start and at ascent drive. However, since the upper limit of rotational speed is low under the type, the maximum speed is restricted low. On the other hand, if the winding specifications are varied to become a xe2x80x9chigh-rotation and low-torquexe2x80x9d type, then this time ability to climbing ascents is reduced, current consumption required in start and in ascent drive increases. Further, current consumption in starting and hill climbing becomes much. That is, by a single motor, it is extremely difficult to simultaneously realize the above two motor characteristics under the condition of constant voltage and the same winding specifications. Further, in the case where the current, the torque and the number of revolution are not matched with appliances, there arises a requirement for establishing such a system that objects of the torque and the number of revolution are obtained by using not a single motor but a reduction gear or the like.
In recent years, a technique named a xe2x80x9cweak fieldxe2x80x9d has appeared, which has effects comparatively similar to the above both characteristics. According to the technique motor advances are electronically changed to realize variable characteristics. For example, in the case of a high-rotation and low-torque motor, angles of advance thereof are made large to change the motor characteristics. However, in this case, although the motor characteristics are certainly changed in a direction required for attaining the object, there is arises a problem of reduction of motor efficiency at the same time. Further, since providing a means for electronically changing the motor advance is needed, there arises a problem of high cost thereof.
On the other hand, in a brushless motor having field windings and using an electromagnet as a filed means, current application to field winding is controlled, and thereby, motor characteristics can be changed by controlling amounts of current flowing in the field windings. Therefore, the problem as described above is not so significant as a problem arising in the motor using a magnet as a field means. However, since all energies required for creating magnetic field depend upon a power supply, an occupation ratio of power required for the field magnetic out of input energies becomes great. Therefore, there arises a problem of reduction of the motor efficiency. In particular, influence thereof remarkably appears in a weak output motor, so that improvement thereof has been desired.
Accordingly, an object of the present invention is to provide a brushless motor that can change characteristics thereof without reducing a motor efficiency.
In order to achieve the above-mentioned object, a brushless motor of the present invention, having a stator around which an armature coil is wound; a rotor rotatably arranged inside or outside said stator; a rotor position detecting means for detecting a position of said rotor; and a current control means for making a current flowing into said armature coil such that a rotating magnetic field is formed between said armature coil and said rotor in accordance with a detected result of said rotor position detecting means, is characterized by a field magneton including a plurality of permanent magnets provided in said rotor and magnetized at the same pole, and a plurality of control poles made of a magnetic material and arranged between said permanent magnets; a field coil forming a closed magnetic path passing through said control poles; and a motor characteristic control means for changing a motor characteristic by controlling at least one of a direction and an amount of current flowing into said field coil, by changing a magnetic flux that said field coil generates, and by controlling an effective magnetic flux affected between said rotor and said stator.
Further, another brushless motor of the present invention, having a stator constituted such that an armature coil is wound around a stator core having a gap at a central portion thereof; a rotor made of a magnetic material and including a bottomed cylindrical yoke rotatably arranged outside said stator; a rotor position detecting means for detecting a position of said rotor; and a current control means for making a current flowing into said armature coil such that a rotating magnetic field is formed between said armature coil and said rotor in accordance with a detected result of said rotor position detecting means, is characterized by a field magneton including a plurality of permanent magnets provided in said rotor and magnetized at the same pole, and a plurality of control poles made of a magnetic material and arranged between said permanent magnets; a boss rotor made of a magnetic material, provided at the central portion of said rotor to project along an axial direction thereof , and arranged in said gap of said stator so as to have an air gap between said stator and the boss rotor, a field coil arranged in said stator so as to face a bottom portion of said yoke in a state of being wound in a surrounding direction of said boss rotor, and forming a closed magnetic path passing through said boss rotor, said yoke, said control poles and said stator core; and a motor characteristic control means for changing a motor characteristic by controlling at least one of a direction and an amount of current flowing into said field coil, by changing a magnetic flux that said field coil generates, and by controlling an effective magnetic flux affected between said rotor and said stator.
Further, another brushless motor of the present invention, having a stator including a stator core around which an armature coil is wound, and a bracket which holds said stator core and is made of a magnetic material; a rotor made of a magnetic material and including a rotor core rotatably arranged inside said stator; a rotor position detecting means for detecting a position of said rotor; and a current control means for making a current flowing into said armature coil such that a rotating magnetic field is formed between said armature coil and said rotor in accordance with a detected result of said rotor position detecting means, is characterized by a field magneton including a plurality of permanent magnets provided in said rotor and magnetized at the same pole, and a plurality of control poles made of a magnetic material and arranged between said permanent magnets; a magnetic path forming member made of a magnetic material, projected from said rotor core along a diametrical direction thereof, and arranged so as to have an air gap in the space of the stator with a gap between the stator and the magnetic path forming member; a field coil arranged in a side of said stator in a state of being wound in a surrounding direction of said rotor core, and forming a closed magnetic path passing through said rotor core, said control poles, said stator core, said bracket and said magnetic path forming member; and a motor characteristic control means for changing a motor characteristic by controlling at least one of a direction and an amount of current flowing into said field coil, by changing a magnetic flux that said field coil generates, and by controlling an effective magnetic flux affected between said rotor and said stator.
By the above-mentioned constitution, in the motor according to the present invention, it is possible to control widely characteristics thereof by controlling field current without changing winding specifications thereof under the same source supply voltage. Therefore, one motor can be used as a low-rotation and high-torque type or a high-rotation and low-torque type and, further, it is possible to achieve miniaturization of the motor, reduction of current consumption, improvement of degree of freedom in design, and the like.